Zonally resolved water vapour coupling with tropical tropopause temperature: Seasonal and interannual variability, and influence of the Walker circulation

Abstract

Global stratospheric water vapour is strongly coupled to the tropical cold-point tropopause temperatures. We quantified the coupling between temperature and water vapour in the TTL on seasonal and interannual time scale using 10 years of satellite based observations, focusing on the zonal asymmetries arising from the Walker circulation. Tropical region (15° N–15° S) shows near perfect correlation values in the TTL (between ~ 15.5 km to CPT) at ascending branches of Walker circulation, indicating a strong coupling between annual cycles of cold-point and water vapour variability. Descending branches of Walker circulation are characterized by weak temperature-water vapour coupling and local lapse-rate minima at about 1–1.5 km below CPT level. The correlation pattern of deseasonalized anomalies of temperature and water vapour shows a strong zonal asymmetry, with maximum correlation values (r ~ 0.7 to 0.9) in the TTL (between 15 km and cold-point level) over Maritime Continents including western Pacific Ocean (90° E–180° E), and Atlantic Ocean (0–50° W) and minimum values (r ~ 0.2 to 0.4) over eastern Pacific and Indian Ocean. The QBO amplitude in CPT-T is more or less zonally symmetric, with peak value over the Maritime Continent and Atlantic Ocean. During ENSO event, CPT-T over the western Pacific and Maritime Continent are largely influenced with warm anomaly. Associate with this CPT-T variation, large enhancement in WMR100 is noticed over the Indian Ocean between 20° N–20° S latitude. The difference between zonal mean deseasonalized anomalies of WMR100 and SMRcpt show significant fluctuations (± 0.3 ppmv) that are roughly coincide with the Oceanic Nino Index with a 6 month lag.